Ultrasonic atomization uses of electronic ultra-high frequency oscillation principle. In addition, the ultrasonic generator, working with a specific oscillation current frequency, produced a high-frequency power signal and converted the signal toward ultrasonic mechanical vibration through the transducer. Moreover, the ultrasonic vibration is propagated through a medium that needs to be atomized, and it causes the formation of a surface tension wave, which is formed at the gas-liquid interface. Due to ultrasonic cavitation, the surface tension waves produce a liquid molecule force and cause the liquid to become droplets from the liquid surface. This is the primary process of liquid atomization using ultrasonic waves. The ultrasonic atomization can form many droplets size up to the micron level. Ultrasonic atomization has many advantages in the field of agricultural engineering because it can form small droplets and has a wide range of applications in the field of agricultural engineering. High-frequency ultrasonic atomization (working frequency above 1 MHz) can change the physical and chemical properties of the atomized liquid to a large extent. Therefore, it is not suitable for the field of atomization cultivation (Aeroponics system) and plant protection. However, low-frequency ultrasonic atomization has less of an effect on the physical and chemical properties of the atomized liquid. However, the main problem associated with low-frequency ultrasonic atomization is that it forms droplets that are too large, resulting in reduced adhesion on the leaves and roots of crops.
A large number of research studies have shown that the charge can reduce the liquid surface tension and atomization resistance. Moreover, when the droplets carry the same charge, under the action of an electric field, it will break the large liquid molecules into smaller droplets with more uniform diameter distribution. Electrostatic atomization has been widely used in many applications including pesticide spraying, industrial spraying, material preparation, fuel combustion, industrial dust collection, desulfurization, particle aggregation and separation. The advantage of electrostatic spray is that the droplet adhesion characteristics are excellent. However, because of technical constraints, the electrostatic voltage of the critical voltage is between several kilo-volts to tens of thousands volts, which is called high-voltage electrostatic atomization. High-voltage electrostatic atomization has the following shortcomings: the voltage is between several kilo-volts to tens of kilo-volts, which is a great security risk for the operator; high-voltage static electricity beyond a certain extent will hurt crops, while low-voltage static electricity will promote the growth of crops; the structure of high-voltage electrostatic spray is complex and requires high cost manufacturing materials, especially those with good insulation properties; the most important thing is that the high-voltage static electricity requires high cost equipment.